Histamine release from mast cells and blood basophils is being studied as one of the immunological mechanisms involved in inflammation. Among the histamine releasing agents employed are IgE antibody, environmental antigens, and the complement factor C5a derived from human serum. The relationships between IgE crosslinking, basophil desensitization and histamine release were analyzed by kinetic studies. Cultured rat basophilic leukemia cells are used as a model for the studies of the IgE receptor, changes in phospholipid methylation in the cells and the role of lymphokines in modulating histamine release.